This invention relates to vehicle wheel alignment and more particularly to vehicle wheel alignment systems for use with vehicles which utilize shims to simultaneously adjust the camber and toe of a vehicle wheel.
For example, tapered full contact rear shims are used to adjust the camber and toe of the rear wheels of certain vehicles. These shims are mounted between the spindle backing plate and the end of the rear axle assembly. The taper of these shims changes the angle between the spindle and the axle, thereby adjusting both toe and camber. A separate shim is required for each wheel.
Various shims and shim systems arc known for simultaneously adjusting both camber and toe of a vehicle wheel. Among them are those shown the following U.S. Patents U.S. Pat. No. 5,129,669 to Specktor; U.S. Pat. No. 5,110,151 to Blechschmidt et. al.; U.S. Pat. No. 5,098,117 to Specktor et al.; U.S. Pat. No. 5,080,388 to Berry et al.; U.S. Pat. No. 5,074,578 to Grove et al.; U.S. Pat. No. 5,046,753 to Giovanni; U.S. Pat. No. 5,044,659 to Specktor et al.; U.S. Pat. No. 5,007,658 to Blechschmidt et al.; U.S. Pat. No. 4,973,075 to Rori et al.; U.S. Pat. No. 4,872,699 to Grove et al.; U.S. Pat. 4,684,150 to Specktor et al. These shims and shim systems in most cases accurately correct both toe and camber, but they could be improved.
It has been found that there are circumstances in which both camber and toe cannot be simultaneously corrected by some shims. By way of illustration, many shims come in fixed sizes, with fixed increments (1/4.degree. or 1/8.degree. typically) between sizes. With a fixed taper, it is often not possible to correct both camber and toe perfectly. No matter how installed, there will be some residual error in toe, or camber, or both, with these shims. Some priority must be assigned, therefore, to toe and camber error to determine what shim and orientation to use. Alignment equipment is available which has a preset priority or allocation of toe and camber error. Such a priority might be, for example, one which weights the errors in a preset fashion (for example, weighting toe error as three times more significant than camber error) and minimizes the total error (the sum of the weighted toe residual error and the weighted camber residual error).
In such equipment, it would be desirable for the residual error of both toe and camber to be displayed to the technician/user, so the user could be aware of the existence, direction and magnitudes of the errors. On occasion the user may prefer a different allocation of residual error between toe and camber. For example, the user may prefer an adjustment which results in zero residual error in toe, while letting the camber residual error increase, or vice versa. Presently available equipment is not believed to provide the technician with this capability. Moreover, if such a feature were available, it would be highly desirable to display to the technician the resulting residual error in camber (or toe) if the preset allocation of residual errors is changed. Moreover, the display of such residual errors should occur in substantially real time, to give the technician useful, timely information concerning the effect of his or her proposed action.
There may be certain orientations for shim installation which are more convenient for the technician than others. A bolt may interfere with installation in the orientation determined by the system, for example, in the case of certain shims. The technician faced with this situation may have a choice concerning how best to approximate the desired orientation, but at present it is not believed that the technician is provided with any information concerning the effect of installing the shim at a slightly different orientation. It would be very desirable to have a display of residual errors which would result from installation at any orientation desired by the technician. Moreover, certain vehicles include provisions (such as an adjustable cam) for adjusting toe independently of any adjustment caused by installation of a shim. For those vehicles, a technician may desire to correct camber with the shim, while leaving most of the correction of toe to the other procedure.
On occasion, the technician may not have available the exact size shim required. It would be advantageous to the user to select another size shim which is in stock, so long as the residual errors resulting from the substitute shim could be easily and readily displayed to determine the acceptability of the proposed substitution. Currently, large charts are available which indicate which size shims to use for particular situations, but these charts are of limited utility in connection with determining appropriate substitute shims.
Even when the technician has the proper size shim in stock, it is not always easy to determine the proper orientation of the shim for installation. It would be highly desirable to have a "life sized" representation of the proper shim in the proper orientation to assist the technician in installing the shim properly. Such representations (whether on a computer screen or on paper) are not generally provided by current systems.
There are adjustable shims which overcome some of the difficulties discussed above. These are two-piece shims which can be rotated, one relative to the other, such that the shim has the correct taper for accurate adjustment of both camber and toe. The entire shim is then rotated to the correct orientation angle and installed. Such shims have adjustable taper. That is, they are not limited to the discrete values of taper found in one-piece shims. They, therefore, normally provide "perfect" adjustments, provided that the changes required are not so large that the shim cannot provide enough change.
It has been found, however, that rotating the two pieces of the adjustable shims to exactly the correct position in not a trivial undertaking. The determination of the proper position of the two pieces may be made by the system, but it is the technician that must make the actual change. In performing this operation it is very important that an actual size representation of the two-piece shim be made available to the user to assist in the proper orientation of the two pieces. A display on a screen or on paper which is of a different size than the actual shim itself is of only limited assistance in making this adjustment.